Substrate processing method and method of manufacturing crystalline silicon carbide (SIC) substrate

ABSTRACT

The present invention provides a method of processing a substrate and a method of manufacturing a silicon carbide (SiC) substrate in which, when annealing processing is performed on a crystalline silicon carbide (SiC) substrate, the occurrence of surface roughness is suppressed. A substrate processing method according to an embodiment of the present invention includes a step of performing plasma irradiation on a single crystal silicon carbide (SiC) substrate ( 1 ) and a step of performing high temperature heating processing on the single crystal silicon carbide (SiC) substrate ( 1 ) in which the plasma irradiation is performed.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation application of InternationalApplication No. PCT/JP2010/054437, filed Mar. 16, 2010, which claims thebenefit of Japanese Patent Application No. 2009-076313, filed Mar. 26,2009. The contents of the aforementioned applications are incorporatedherein by reference in their entities.

TECHNICAL FIELD

The present invention relates to a method of preprocessing a crystallinesilicon carbide (SiC) substrate such as of single crystal siliconcarbide (SiC) and a method of manufacturing the crystalline siliconcarbide (SiC) substrate. More particularly, the present inventionrelates to a technology for acquiring surface flatness by preprocessingin a method of heat-treating the substrate.

BACKGROUND ART

In order to electrically activate an impurity implanted into a singlecrystal silicon carbide (SiC) substrate, an activation annealingprocessing process is performed at a high temperature. However, when theimpurity in the silicon carbide (SiC) substrate is subjected toactivation annealing, the surface roughness of the substratedisadvantageously occurs.

As methods of solving this problem, a method of adding a silane (SiH₄)gas to perform annealing (see non-patent document 1), a method ofapplying a carbon coating to a substrate to be processed to performannealing (see patent document 1) and a method of performing annealingunder an atmosphere in which the partial pressure of the remaining wateris reduced in a high vacuum region (see patent document 2) are known.Patent document 3 discloses that an epitaxial layer is formed on asubstrate, an ion implantation layer is formed on a surface of theepitaxial layer, high temperature annealing for the activation of animpurity is performed and thereafter the surface (the surface of the ionimplantation layer) of the single crystal silicon carbide (SiC)substrate is subjected to plasma etching using plasma.

-   [Patent document 1] Japanese Patent Application Laid-open No.    2005-39257-   [Patent document 2] International Publication No. 08/136,126    Pamphlet-   [Patent document 3] Japanese Patent Application Laid-open No.    2001-35838-   [Non-patent document 1] M. A. Capano, S. Ryu, J. A. Cooper, J    R., M. R. Melloch, K. Rottner, S. Karlsson, N. Nordell, A. Powell.    and D. E. Walker: J. Electron. Mater, P214-218, Vol. 28, No. 3.    (1999)

SUMMARY OF INVENTION

However, in the substrate heat treatment device and the heat treatmentmethod described in non-patent document 1, since it is very difficult tocontrol additive amount of silane (SiH₄) gas, there is such a problemthat a droplet (liquefied and aggregated silicon) of silicon (Si) mayoccur, or that the change in the amount of water brought from thesubstrate makes it difficult to ensure reproducibility of maintainingsurface flatness of a silicon carbide (SiC) sample after activationannealing.

In the substrate heat treatment device disclosed in patent document 1,since a substrate to be processed is coated with a resist and iscarbonized in a special high-temperature furnace, and thus the substrateto be processed is carbon-coated, the number of processes is increased,and there is a concern of contamination by heavy metals from the resist.

The technology disclosed in patent document 2 is an effective technologyin that the partial pressure of the remaining water under an annealingatmosphere is controlled during the annealing and thus it is possible toreduce the surface roughness (RMS value) of the substrate, that is, thesurface flatness of silicon carbide (SiC); the technology sufficientlyachieved electrical activation required in those times. However, inconsideration of enhancement of yield and the like, it is desirable toachieve further enhanced surface flatness.

In the substrate heat treatment method disclosed in patent document 2,when aluminum (Al) is implanted as an impurity, a very high temperatureof about 1900° C. is required to achieve an activation rate of 100%; inthis case, step bunching is not observed but holes such as pits may belocally produced, and this may cause a leak in a pn junction.

In the technology disclosed in patent document 3, high temperatureannealing processing for activating the implanted impurity is performed,and thereafter step bunching and protrusions and recesses formed in thesurface of the substrate (the surface of an ion implantation layer),abnormal deposition materials deposited on the surface of the substrateor portions whose compositions have been changed are physically removedby plasma etching. In patent document 3, the surface of the substrate isremoved by plasma etching with a thickness of 120 nm or 0.1 μm.

In the technology disclosed in patent document 3, in order to achievethe technological purpose of removing effects after the annealing suchas abnormal deposition materials on the SiC surface, composition change,the change in the shape of the surface (surface flatness) and the like,it is necessary to remove, by etching, part of the surface (the surfacewhere the change in the shape of the surface or the like is produced) ofthe ion implantation layer that is the surface layer of the SiCsubstrate. Hence, if the thickness of the ion implantation region (animpurity region) is not increased, the ion implantation region that hasbeen formed with difficulty may disappear. In other words, when theimpurity region has a small thickness, the entire ion implantationregion may be cut.

Therefore, in patent document 3, it is necessary to form the ionimplantation region thicker than the thickness of the necessary ionimplantation region, by a thickness corresponding to a portion removedby the plasma etching. In other words, it is necessary to form the ionimplantation region that has not only an originally required amount(thickness) but also an extra thickness; in consideration of cost andyield, it is required to achieve the flatness of the surface of thesingle crystal silicon carbide (SiC) substrate while reducing theamounts of epitaxial layer and impurity used for formation of the extraion implantation region.

The present invention is made in view of the foregoing problem; anobject of the present invention is to provide a method of processing asubstrate in which, when a crystalline silicon carbide (SiC) substrateis subjected to annealing processing, the occurrence of the surfaceroughness is suppressed and a method of manufacturing the siliconcarbide (SiC) substrate.

To achieve the above object, the present invention is a method ofprocessing a crystalline silicon carbide (SiC) substrate, and the methodincludes: a step of performing plasma irradiation using a gas containingat least one of an inert gas and a fluorine based gas on the crystallinesilicon carbide (SiC) substrate in which an impurity atom ision-implanted; and a step of performing high temperature heatingprocessing on the crystalline silicon carbide (SiC) substrate on whichthe plasma irradiation is performed.

Further, the present invention is a method of manufacturing acrystalline silicon carbide (SiC) substrate, and the method includes: astep of preparing a crystalline silicon carbide (SiC) substrate in whicha predetermined impurity atom is ion-implanted; a step of performingplasma irradiation using a gas containing at least one of an inert gasand a fluorine based gas on the crystalline silicon carbide (SiC)substrate; and a step of performing high temperature heating processingon the crystalline silicon carbide (SiC) substrate on which the plasmairradiation is performed.

Furthermore, the present invention is a method of processing acrystalline silicon carbide (SiC) substrate, and the method includes: astep of performing plasma irradiation on the crystalline silicon carbide(SiC) substrate so as to remove at least part of a substance, other thanthe crystalline silicon carbide (SiC) substrate, the substance beingpresent on a surface of the crystalline silicon carbide (SiC) substrate;and a step of performing high temperature heating processing on thecrystalline silicon carbide (SiC) substrate on which the plasmairradiation is performed.

Still further, the present invention is a method of manufacturing acrystalline silicon carbide (SiC) substrate, and the method includes: astep of preparing a crystalline silicon carbide (SiC) substrate in whicha predetermined impurity atom is ion-implanted; a step of performingplasma irradiation on the crystalline silicon carbide (SiC) substrate soas to remove at least part of a substance, other than the crystallinesilicon carbide (SiC) substrate, the substance being present on asurface of the crystalline silicon carbide (SiC) substrate; and a stepof performing high temperature heating processing on the crystallinesilicon carbide (SiC) substrate on which the plasma irradiation isperformed.

According to the substrate processing method and the method ofmanufacturing the crystalline silicon carbide (SiC) substrate of thepresent invention, when the high temperature heating processing (forexample, annealing processing) is performed on the crystalline siliconcarbide (SiC) substrate, it is possible to reduce the surface roughnesson the crystalline silicon carbide (SiC) substrate on which the hightemperature heating processing is performed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a substrate processing method according toan embodiment of the present invention;

FIG. 2 is a surface observation diagram after annealing processing incomparative example 1 of the present invention;

FIG. 3 is a surface observation diagram after annealing processing incomparative example 2 of the present invention;

FIG. 4 is a surface observation diagram after annealing processing inexample 1 of the present invention;

FIG. 5 is a surface observation diagram after annealing processing inexample 2 of the present invention;

FIG. 6 is a surface observation diagram after annealing processing inexample 3 of the present invention;

FIG. 7 is a surface observation diagram after annealing processing inexample 4 of the present invention; and

FIG. 8 is a surface observation diagram after annealing processing inexample 5 of the present invention.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention will be described in detailbelow. Components described in the embodiment are only illustrative; thetechnical scope of the present invention is defined by claims and is notlimited by the embodiment below.

An example of a substrate processing method according to the presentinvention will be described with reference to FIG. 1.

(Substrate Processing Method 1)

As a substrate of single crystal silicon carbide (SiC), a samplesubstrate obtained by growing a p-type SiC epitaxial layer 10micrometers by CVD on a single crystal silicon carbide (4H—SiC (0001))substrate is RCA-washed and is then used. Hence, in the initial step ofFIG. 1, a single crystal silicon carbide (SiC) substrate 1 on which ap-type SiC epitaxial layer 2 is formed is prepared.

The first step is a step of forming a buffer layer 3 on a single regionincluding the surface of the p-type SiC epitaxial layer 2. A siliconoxide (SiO₂) buffer layer 3 of ion implantation is formed by conductingsacrificial oxidation under an atmosphere of dry oxygen (O₂) at atemperature of 1150° C. for 30 minutes such that an oxide film is 10 nmthick.

The second step is a step of implanting nitrogen (N⁺) ions 5 as animpurity atom into an ion implantation region 4 of the single crystalsilicon carbide (SiC) substrate. The ion implantation is performed atroom temperature at multiple stages of implantation energy of 15 keV to120 keV to achieve a box profile on condition that the amount ofimplantation is 4×10¹⁹/cm³ and the depth is 250 nm.

Instead of nitrogen (N), the impurity atoms to be implanted may be anyof phosphorus (P), aluminum (Al) and boron (B).

In the third step, the silicon oxide (SiO₂) layer that is the bufferlayer 3 is removed by hydrofluoric acid.

The fourth step is a step of irradiating plasma to the surface of thesingle crystal silicon carbide (SiC) substrate (the ion implantationregion 4). The plasma irradiation is performed by an inductively coupledplasma (ICP) etcher using argon (Ar) gas, a mixed gas of argon (Ar) gasand carbon tetrafluoride (CF₄) gas or carbon tetrafluoride (CF₄) gas.Here, the plasma irradiation is preferably performed such that theetched amount (SiC etching amount) is 20 nm or less.

In the fifth step, the single crystal silicon carbide (SiC) substrate onwhich the plasma irradiation has been performed in the fourth step iscleaned (washed) by RCA washing.

The sixth step is a step of performing high temperature heatingprocessing (activation annealing processing) on the single crystalsilicon carbide (SiC) substrate on which the plasma irradiation has beenperformed. In this step, the activation annealing processing isperformed on the single crystal silicon carbide (SiC) substrate 1 havingthe p-type SiC epitaxial layer 2 on which the plasma irradiation hasbeen performed in the fourth step and the ion implantation region 4 hasbeen formed either in a high-frequency induction heating furnace at atemperature of 1700° C. for ten minutes or in an electron bombardmentvacuum heating device at a high temperature of 1900° C. for one minute.

By the manufacturing method described above, in the embodiment of thepresent invention, it is possible to manufacture the single crystalsilicon carbide (SiC) substrate in which surface roughness and theformation of pits are suppressed.

Although, in the present embodiment, as the method of plasma irradiationin the fourth step, the ICP etcher is used, the present invention is notlimited to this method. As long as a method of generating plasma isused, any method may be used such as a capacitive coupling type using aparallel plate method, a microwave excitation type or an RF downstreamtype.

Although, in the present embodiment, as the high temperature heatingmethod in step 6, examples of the high-frequency induction heatingmethod and the electron bombardment vacuum heating method are described,as long as a method in which heating processing such as annealingprocessing can be performed is used, any heating method may be used suchas an infrared heating method, a hybrid heating method of infraredheating and high-frequency induction heating or a resistance heatingmethod.

Although, in the first and fourth steps, the RCA washing is performed,the washing is not limited to the RCA washing. If it is not necessary,the washing may be omitted.

(Substrate Processing Method 2)

Another example of the substrate processing method according to thepresent invention will be described.

In the present embodiment, the first step (the formation of the bufferlayer) and the third step (the removal of the buffer layer) of thesubstrate processing method 1 are omitted.

Example 1

By the substrate processing method 1, the substrate processing method ofthe single crystal silicon carbide (SiC) substrate was performed. Theplasma irradiation by the inductively coupled plasma (ICP) etcher in thefourth step was performed using a mixed gas of argon (Ar) gas and carbontetrafluoride (CF₄) gas under conditions shown in table 1.

TABLE 1 RF power of an upper coil 400 W Substrate bias 150 W CF₄ gasflow rate 30 sccm Ar gas flow rate 20 sccm Etching pressure 0.2 PaPlasma irradiation period 10 seconds SiC etching amount 20 nm

In the high temperature heating processing in the fifth step, theactivation annealing processing was performed using a high-frequencyinduction heating furnace at a temperature of 1700° C. for ten minutes.

The surface roughness (RMS value: root mean square value) of theobtained substrate was measured using an atomic force microscope (AFM:atomic force microscopy). The measurement was performed in a dampingforce mode over a measurement area of 4 micrometers×4 micrometers.

FIG. 4 is a surface observation diagram after annealing processing inthe present example. When the surface roughness was observed by AFM, theRMS value was 1.6 nm; it has been found that the preprocessing by theplasma irradiation before the annealing processing has the effect ofreduction in the surface roughness when the high temperature processingis performed on the single crystal silicon carbide (SiC) (FIG. 4).

As described above, in the present example, it has been found from table1 and FIG. 4 that even when the amount of etching by the plasmairradiation before the annealing processing is 20 nm, it is possible toreduce the surface roughness. It is therefore possible to reduce theamount of etching of the ion implantation region formed on the singlecrystal silicon carbide (SiC) substrate and to reduce the formation ofthe extra ion implantation region.

The surface roughness (RMS) was measured with the following device.

Atomic force microscope (AFM: atomic force microscopy)

-   -   NPX200M0001 made by Seiko Instruments Inc.

Observation head NPX200

Controller Nanopics 2100

Scanning in a damping force mode (DFM)

(in the mode in which the distance between a cantilever and a specimensurface is controlled such that a probe vibrating cyclically at aconstant amplitude is brought close to a substrate specimen surface, andthat the amount of reduction of the amplitude is constant)

Example 2

In order to reduce the amount of etching of the silicon carbide (SiC)substrate by the plasma irradiation, the substrate processing wasperformed under conditions shown in table 2, instead of using the plasmaconditions of the inductively coupled plasma (ICP) etcher in the fourthstep in example 1.

TABLE 2 RF power of the upper coil 400 W Substrate bias 0 W CF₄ gas flowrate 30 sccm Ar gas flow rate 20 sccm Etching pressure 0.2 Pa Plasmairradiation period 60 seconds SiC etching amount 0 nm

FIG. 5 is a surface observation diagram after annealing processing inthe present example. When the surface roughness was observed by AFM, theRMS value was 1.6 nm; it has been found that the preprocessing by theplasma irradiation before the annealing process has the effect ofreduction in the surface roughness when the high temperature processingis performed on the single crystal silicon carbide (SiC) (FIG. 5).

As described above, in the present example, it has been found from table2 and FIG. 5 that even when the amount of etching by the plasmairradiation performed before the annealing processing is 0 nm, it ispossible to reduce the surface roughness. It is therefore possible toreduce the surface roughness without the actual formation of the extraion implantation region.

Example 3

In order to evaluate the flow rate ratio of a process gas by the plasmairradiation, the substrate processing was performed under conditionsshown in table 3, instead of using the plasma irradiation conditions bythe inductively coupled plasma (ICP) etcher in the fourth step inexample 1.

TABLE 3 RF power of the upper coil 400 W Substrate bias 0 W CF₄ gas flowrate 0 sccm Ar gas flow rate 20 sccm Etching pressure 0.2 Pa Plasmairradiation period 60 seconds SiC etching amount 0 nm

FIG. 6 is a surface observation diagram after annealing processing inthe present example. When the surface roughness was observed by AFM, theRMS value was 2.1 nm; it has been found that, although the preprocessingby the plasma irradiation before the annealing processing with only theargon (Ar) gas has a small effect as compared with the case where thecarbon tetrafluoride (CF₄) gas was added, the preprocessing has theeffect of reduction in the surface roughness when the high temperatureprocessing is performed on the single crystal silicon carbide (SiC)(FIG. 6).

As described above, in the present example, it has been found from table3 and FIG. 6 that even when the amount of etching by the plasmairradiation performed before the annealing processing is 0 nm, it ispossible to reduce the surface roughness. It is therefore possible toreduce the surface roughness without the actual formation of the extraion implantation region.

Example 4

Furthermore, in order to evaluate the process gas flow rate ratio in theplasma irradiation, the substrate processing was performed underconditions shown in table 4, instead of using the plasma irradiationconditions by the inductively coupled plasma (ICP) etcher in the fourthstep in example 1.

TABLE 4 RF power of the upper coil 400 W Substrate bias 0 W CF₄ gas flowrate 30 sccm Ar gas flow rate 0 sccm Etching pressure 0.2 Pa Plasmairradiation period 60 seconds SiC etching amount 0 nm

FIG. 7 is a surface observation diagram after annealing processing inthe present example. When the surface roughness was observed by AFM, theRMS value was 0.9 nm; it has been found that, the plasma irradiationbefore the annealing processing with only the carbon tetrafluoride (CF₄)gas has the significant effect of reduction in the surface roughnesswhen the high temperature processing is performed on the single crystalsilicon carbide (SiC) (FIG. 7).

As described above, in the present example, it has been found from table4 and FIG. 7 that even when the amount of etching by the plasmairradiation performed before the annealing processing is 0 nm, it ispossible to reduce the surface roughness. It is therefore possible toreduce the surface roughness without the actual formation of the extraion implantation region.

Example 5

In order to evaluate the effect obtained by performing the hightemperature heating processing using the electron bombardment heatingmethod under a vacuum atmosphere, the same substrate processing as inexample 4 was performed instead of performing the high temperatureheating processing in the fifth step using the electron bombardmentheating device under a vacuum of 1×10⁻³ Pa at a temperature of 1900° C.for one minute.

FIG. 8 is a surface observation diagram after annealing processing inthe present example. When the surface roughness was observed by AFM, theRMS value was 0.80 nm, and no minute pit was observed (FIG. 8). It hasbeen found that, the plasma irradiation with only the carbontetrafluoride (CF₄) gas has the significant effect of reduction in thesurface roughness when the high temperature processing is performed onthe single crystal silicon carbide (SiC).

As described above, in the present example, it has been found from table4 and FIG. 8 that even when the amount of etching by the plasmairradiation performed before the annealing processing is 0 nm, it ispossible to reduce not only the surface roughness but also thegeneration of pits. It is therefore possible to reduce the surfaceroughness and the generation of pits without the actual formation of theextra ion implantation region.

Comparative Example 1

The processing on the silicon carbide (SiC) substrate was performed inthe same method as in example 1 except that the fourth step (the plasmairradiation) was not performed.

FIG. 2 is a surface observation diagram after annealing processing incomparative example 1. As is obvious from an AFM image shown in FIG. 2,in comparative example 1, the RMS value indicating the surface roughnesswas 6.6 nm, and step bunching that was significant surface roughness wasobserved.

Comparative Example 2

The processing on the silicon carbide (SiC) substrate was performed inthe same method as in example 5 except that the fourth step (the plasmairradiation) was not performed.

FIG. 3 is a surface observation diagram after annealing processing incomparative example 2. As is obvious from an AFM image shown in FIG. 3,in comparative example 2, the RMS value indicating the surface roughnesswas reduced to 1.57 nm and no step bunching was observed but 23 minutepits were observed.

As is obvious from examples 1 to 5 and comparative examples 1 and 2above, in the embodiment of the present invention, the plasmairradiation is performed on the single crystal silicon carbide (SiC)substrate before the high temperature heating processing (for example,annealing processing) is performed on the single crystal silicon carbide(SiC), and thus it is possible to reduce the surface roughness and theformation of pits. Since, as described above, in the embodiment of thepresent invention, it is possible to reduce not only the surfaceroughness but also the formation of pits, it is possible to reduce theoccurrence of a leak in a pn junction and enhance yield in themanufacturing of the silicon carbide (SiC) substrate. The plasmairradiation is preferably performed using at least one of an inert gassuch as argon (Ar) and a fluorine based gas such as carbon tetrafluoride(CF₄).

Example 6

The same substrate processing as in example 1 was performed except that,instead of the silicon carbide (4H—SiC (0001)) substrate having theepitaxial layer 2 formed by epitaxial growth, as a substrate, the singlecrystal silicon carbide (4H—SiC (0001)) substrate was used. When thesubstrate was compared with a substrate obtained by performing thesubstrate processing method in which the plasma irradiation in step 4was excluded, it is possible to reduce the surface roughness.

Example 7

The substrate processing was performed by the substrate processingmethod 2. When the substrate was compared with a substrate obtained byperforming the substrate processing method in which the plasmairradiation was not performed, the surface roughness was reduced.

As described above, according to the present invention, with thepreprocessing by the plasma irradiation, it is possible to reduce thesurface roughness and the generation of pits caused when the hightemperature heating processing is performed on the single crystalsilicon carbide (SiC) or the silicon carbide (SiC) obtained by epitaxialgrowth on the single crystal silicon carbide (SiC) substrate. Thus, itis possible to enhance yield of the silicon carbide (SiC) device.

The reason why performing the plasma irradiation before the hightemperature heating processing such as the annealing processing reducedthe surface roughness and the generation of pits is not clear; this isprobably because impurities such as silicon oxide carbide (SiOC) and thelike adhering to or formed on the substrate are removed by the plasmairradiation, and thereby the facilitation of a surface chemical reactionby the impurities at the time of high temperature heating wassuppressed.

Anyway, when the impurity implanted into the single crystal siliconcarbide (SiC) substrate is electrically activated by performing the hightemperature processing, the plasma irradiation is performed on thesingle crystal silicon carbide (SiC) substrate before the hightemperature processing is performed, and thus it is possible to reducethe formation of factors for degrading the flatness of the surface ofthe substrate, such as step bunching or pits.

As described above, in the present invention, it is important to performthe plasma irradiation processing before the high temperature heatingprocessing such as the annealing processing; it is not essential to etchthe substrate by performing the plasma irradiation processing. In thepresent invention, in the stage preceding the high temperature heatingprocessing, the plasma irradiation is performed on the silicon carbide(SiC) substrate before the high temperature heating processing so thatthe surface of the substrate is processed to minimize the formation ofthe factors for degrading the flatness caused by the high temperatureheating processing, that is, the front-end process for reducing thesurface roughness caused by the high temperature heating processing isperformed before the high temperature heating processing. In otherwords, the plasma irradiation is performed so as to remove at least partof a substance (for example, an impurity such as silicon oxide carbide(SiOC) adhering to or formed on the substrate) other than thecrystalline silicon carbide (SiC) substrate which is present on thesurface of the crystalline silicon carbide (SiC) substrate. Whether partof the crystalline silicon carbide (SiC) substrate is etched (forexample, example 1) or is not etched by the plasma irradiation (forexample, examples 2 to 5), if at least part of the substance, that is,the impurity can be removed, the factors for the surface roughness arereduced, and this results in reducing the generation of step bunchingand pits.

In other words, in the present invention, it is important to perform theplasma irradiation on the substrate in the stage preceding the hightemperature heating processing on the silicon carbide (SiC) substrate;before the high temperature heating processing, by the plasmairradiation, the processing for reducing the generation of the factorsfor degrading the flatness caused by the high temperature heatingprocessing is previously performed on the silicon carbide (SiC)substrate. In the present invention, as described in examples 2 to 5,even if the amount of etching of the silicon carbide (SiC) substrate bythe plasma irradiation is substantially zero, the degradation of thesurface flatness of the substrate surface is suppressed after the hightemperature heating processing. As described above, in the presentinvention, it is not essential to perform the plasma irradiation to etchthe substrate; the plasma irradiation of the present invention isperformed before the high temperature heating processing so as topreviously reduce the surface roughness and the formation of pits on thesubstrate surface before the surface roughness and the formation of pitscaused by the high temperature heating processing are produced.

As described above, the present invention is fundamentally differentfrom the invention for removing, by etching, the change in the surfaceshape such as step bunching that has already been formed after the hightemperature annealing processing, and the factors for causing stepbunching and pits are removed by the plasma irradiation before theheating processing (such as the annealing processing). In other words,the present invention does not remove one region on the silicon carbide(SiC) substrate by etching through plasma. Hence, as in example 1, evenif the amount of etching by the plasma irradiation performed before theheating processing is reduced to 20 nm, it is possible to reduce theformation of step bunching and pits on the surface after the heatingprocessing. Moreover, as in examples 2 to 5, even if the amount ofetching by the plasma irradiation is reduced to 0 nm, it is possible toreduce the formation of step bunching and pits on the surface after theheating processing.

According to the present invention, since the amount of cutting byetching for reduction in surface roughness can be reduced or reduced tozero, it is possible to achieve low cost.

Although the preferred embodiment of the present invention has beendescribed above with reference to the accompanying drawings, the presentinvention is not limited to such an embodiment, and many modificationsare possible in the technical scope grasped from the scope of claims.The present invention is not limited by the above embodiment; manymodifications and variations are possible without departing from thespirit and scope of the invention.

1. A method of processing a crystalline silicon carbide (SiC) substrate,the method comprising: a step of removing an oxide film formed on thecrystalline silicon carbide (SiC) substrate in which an impurity atom ision-implanted; a step of performing plasma irradiation using a gascontaining at least one of an inert gas and a fluorine based gas on thecrystalline silicon carbide (SiC) substrate in which the oxide film isremoved; and a step of performing high temperature heating processing onthe plasma-irradiated crystalline silicon carbide (SiC) substrate. 2.The substrate processing method according to claim 1, wherein thecrystalline silicon carbide (SiC) substrate includes an epitaxialsilicon carbide (SiC) crystalline layer as a surface layer.
 3. Thesubstrate processing method according to claim 1, wherein the gas is anyof argon gas, carbon tetrafluoride gas and a mixed gas of argon gas andcarbon tetrafluoride gas.
 4. The substrate processing method accordingto claim 1, wherein the impurity atom is any of nitrogen (N), phosphorus(P), aluminum (Al) and boron (B).
 5. The substrate processing methodaccording to claim 1, wherein the high temperature heating processing isperformed by a device of a high-frequency induction heating method, anelectron bombardment heating method or a resistance heating method.
 6. Amethod of manufacturing a crystalline silicon carbide (SiC) substrate,the method comprising: a step of preparing a crystalline silicon carbide(SiC) substrate in which a predetermined impurity atom is ion-implanted;a step of removing an oxide film formed on the crystalline siliconcarbide (SiC) substrate; a step of performing plasma irradiation using agas containing at least one of an inert gas and a fluorine based gas onthe crystalline silicon carbide (SiC) substrate in which the oxide filmis removed; and a step of performing high temperature heating processingon the plasma-irradiated crystalline silicon carbide (SiC) substrate. 7.The method of manufacturing a crystalline silicon carbide (SiC)substrate according to claim 6, wherein the crystalline silicon carbide(SiC) substrate is a single crystal silicon carbide (SiC) substrate. 8.The method of manufacturing a crystalline silicon carbide (SiC)substrate according to claim 7, wherein the single crystal siliconcarbide (SiC) substrate includes an epitaxial silicon carbide (SiC)crystalline layer as a surface layer.
 9. The method of manufacturing acrystalline silicon carbide (SiC) substrate according to claim 6,wherein the gas is any of argon gas, carbon tetrafluoride gas and amixed gas of argon gas and carbon tetrafluoride gas.
 10. The method ofmanufacturing a crystalline silicon carbide (SiC) substrate according toclaim 6, wherein the step of preparing the silicon carbide (SiC)substrate includes a step of ion-implanting the predetermined impurityatom into the crystalline silicon carbide (SiC) substrate.
 11. Themethod of manufacturing a silicon carbide (SiC) substrate according toclaim 10, wherein the step of preparing the crystalline silicon carbide(SiC) substrate further includes, before the step of ion-implanting, astep of performing sacrificial oxidation on a portion including asurface of the crystalline silicon carbide (SiC) substrate to form abuffer layer for the ion implantation.
 12. A method of manufacturing acrystalline silicon carbide (SiC) substrate, the method comprising: astep of preparing a crystalline silicon carbide (SiC) substrate in whicha predetermined impurity atom is ion-implanted; a step of removing, fromthe crystalline silicon carbide (SiC) substrate, an oxide film formedthereon; a step of performing plasma irradiation on the crystallinesilicon carbide (SiC) substrate so as to remove at least part of asubstance, other than the crystalline silicon carbide (SiC) substrate,the substance being present on a surface of the crystalline siliconcarbide (SiC) substrate in which the oxide film is removed; and a stepof performing high temperature heating processing on theplasma-irradiated crystalline silicon carbide (SiC) substrate.